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Under-sowing cover crops into maize

Insights27 May 2016

A new technique designed to protect maize stubbles from soil erosion and leaching over winter has been developed and trialled with success in the Welsh borders.

The technique – involving the under-sowing of a cover crop into maize – could be replicated throughout the UK and make a significant contribution to the performance and acceptability of the crop from an environmental perspective.

Adding the cover crop – usually Italian or perennial rye-grass – at precisely the right time and stage of the maize’s growth, could help growers comply with greening rules, meet the requirements of cross-compliance and significantly cut the pollution of water courses with leached nitrogen, other minerals and silt.

By completing the under-sowing at the right time and using the right techniques, trials have shown the under-sown crop has the potential to produce up to three tonnes of dry matter per hectare. This can then be grazed or ploughed in as green manure, which will aid soil organic matter, structure and fertility.

This has been achieved without significant impact on maize yields. The technique has emerged from a collaborative project involving the Wye and Usk Foundation, Welsh Water, Cranfield University and seed and agronomy specialists Field Options who worked with a local contractor and farmer.

The group has also been inspired by practices in Denmark, where maize is widely under-sown.

However, purpose-built equipment is not available in the UK, so the team has now developed bespoke kit which could be replicated by other contractors or taken up by machinery manufacturers in the UK.

Francis Dunne of Field Options, who coordinated the project, says: “We built the equipment on a frame and disc coulters from Weaving Machinery, adding an air seeder unit from Stocks AG.

“We felt it was important to develop a drill as Danish trials suggest establishment can be greatly enhanced by drilling the seed with disc coulters, consolidated by a press wheel. Broadcasting the seed or broadcasting and harrowing is much less reliable, especially when conditions are dry which can compromise performance.

“The drill – built by Powys-based contractor, Roy Price – is a specialist tool for use by a specialist contractor whose tractor tyres and wheel spacings are set up for this purpose.

“It is set up to drill into crops planted with a six row maize drill with standard spacing [75cm or 30 inch], drilling three rows of grass between each row of maize. Tolerances have been built in to allow for its use in maize sown with an eight row drill.”

A key to the success of the process is said to be the timing of drilling which should be undertaken once the maize has established but when it is still short enough to drive through.

“This means drilling between the rows five to seven days after the last herbicide application, which is normally between the three to four and 10-leaf stage of the crop,” says Mr Dunne. “This provides a narrow window and is likely to mean going from late May through to early July, depending on when the maize was sown.”

In the 2015 trials, maize was under-sown under three different herbicide regimes and the process was said to have been successful in every case.

“We knew there was a risk the herbicides could affect the establishment of the cover crop, but our work has suggested neither mesotrione nor pendimethalin affect the establishment of vigorous Italian rye-grass,” he says.

“But our advice is to work with your agronomist, control problem perennial weeds prior to growing maize and do not under-sow fields known to have problem weeds which may need a late herbicide.”